The present invention relates to generally an exhaust gas recirculation system for recirculating the exhaust gases from an exhaust system to an intake system of an internal combustion engine in order to minimize the contents of nitrogen oxides in the exhaust gases, and more particularly a flow control valve for controlling the flow rate of the recirculated exhaust gases in the exhaust gas recirculation system.
In the conventional exhaust gas purifying system, a flow control valve, which controls the flow rate of the recirculated exhaust gases, is opened in response to the pressure of the recirculated exhaust gases and is closed by the pressure of the secondary air supplied to an exhaust gas purifying system such as a thermal reactor when the speed of an automotive vehicle exceeds a predetermined speed or when the temperature of the engine exceeds a predetermined temperature. However, the pressure of secondary air is considerably decreased when a line for charging secondary air to a flow control valve is damaged, when the secondary air is bypassed or when a magnet clutch type air pump is used. As a result the flow control valve cannot interrupt the recirculation of exhaust gases so that the exhaust gases are recirculated into the intake system, thus adversely affecting the engine operation.